Ph.D. Student Caleb Broodo is Analyzing High-Energy Particle Collisions at Brookhaven National Lab

Learning more about the properties of extreme matter – created through high-energy particle collisions approaching the speed of light and analyzed with the help of sophisticated advanced computing – might seem the stuff of science fiction, but it’s Caleb Broodo’s day job.

Broodo, a physics Ph.D. student at the University of Houston’s College of Natural Sciences and Mathematics, is spending a year at Brookhaven National Laboratory in New York as part of the Department of Energy Office of Science Graduate Student Research Program, a selective award giving graduate students access to state-of-the-art facilities and resources at DOE national laboratories.

“We’re looking at matter that’s pushed to its absolute limits,” Broodo said. “Once you figure that out, you have potentially the entire knowledge base of how matter behaves. This is matter that exists on such a small time scale – on the order of microseconds – but its behavior has astronomical implications.”

At Brookhaven, located on Long Island, Broodo works with the Solenoidal Tracker, known as STAR, and part of the Relativistic Heavy Ion Collider (RHIC). STAR is capable of tracking thousands of particles produced by collisions inside the collider.

His goal is to extract the speed of sound in a high-temperature, high-density nuclear medium to determine the physical characteristics of extreme matter and, ultimately, to increase the scientific understanding of the so-called equation of state, or the relationship between pressure, volume, and temperature of a quantity of these particles.

Broodo said that measuring the compressibility of high temperature, high density matter for select collisions at BNL’s Relativistic Heavy-Ion Collider breaks new ground in the field.

The results could yield valuable insights into quark gluon plasma – physicists know the universe was in a quark gluon plasma phase in the microseconds after the Big Bang – as well as providing more information about the matter inside neutron stars.

Access to Expertise

At Brookhaven, Broodo spent a week in the control room, recording collisions of gold particles. Most of his work, however, involves data analysis of information from the collisions of these gold atoms.

To better understand what happens to these particles inside the collider, he is writing code to record various parameters, including how many particles were measured, their momentum and other data points.

“It’s possible when these heavy ions collide, if the circumstances are right, you get this new phase of matter that is characterized by matter pushed to its absolute limit in terms of density and temperature, which is known as the quark gluon plasma,” said Broodo, whose research focuses on heavy ion nuclear physics.

Rene Bellwied, M.D. Anderson Professor of Physics and Broodo’s advisor at UH, said the award offers a valuable opportunity. “Caleb is one of our best students, and the opportunity to not only experience the collection of data firsthand but also to work for an extended period of time in the multi-national research environment with top rated scientists at BNL really allowed him to come into his own as a physicist,” he said.

Bellwied is just one of the people Broodo credits with helping him along the way. Others include Lijuan Ruan, his mentor at Brookhaven and co-spokesperson for STAR; Prithiwish Tribedy, an expert in the STAR collaboration; Rutik Manikandhan, a UH graduate student and a member of the STAR collaboration; and Omar Vasquez-Rueda, a postdoctoral researcher at UH who works with a collaboration at the ALICE detector on the Large Hadron Collider at CERN in Switzerland.

“The great thing about this whole opportunity is resources,” Broodo said. “It’s not necessarily access to the collider, to computers and whiteboards, although all of that is great. It’s the people. You have these technical issues you’re trying to overcome, and it’s one thing to email someone or get on a Skype call. It’s completely different to go into somebody’s office and go to the whiteboard and deliberate.”

The DOE program even allowed him to meet with Barry Barish, now on the faculty at Stony Brook University, who shared the 2017 Nobel Prize in physics for the observation of gravitational waves with the historic Laser Interferometer Gravitational-wave Observatory (LIGO) experiment.

Barish’s career involved other fields of experimental physics. “He helped me understand that the analysis and design skills you learn in one field are translatable to others,” Broodo said. “I look forward to working in the nuclear field later on, but I take comfort in knowing that the frontiers of experimental physics are always accessible to me as long as I am willing to work for it.”

A Slight Shift in Focus

Broodo graduated from UH in 2022 with a degree in electrical engineering – he played center as a walk on for the Cougar basketball team, scoring the first points of his college career during the 2019 NCAA tournament – before pivoting to particle physics for graduate school.

It’s not really such a change in direction, he said. “I work in experimental physics, and there is so much overlap between that and electrical engineering. It was always something that was of interest to me.”

Engineering, of course, is generally focused on solving specific problems, while experimental physics aims for something bigger.

While Broodo’s project could lead to a better understanding of the formation of the universe, it’s also about expanding fundamental knowledge. “Its technological capacity, if any, will not be realized for another century. We’re somewhat like Michael Faraday in the early 1800s, a (British) physicist who explored the nature of electric charges and fields, decades before the onset of the lightbulb or the radio would show its potential.”

It’s hard to see now, he said, “but perhaps someday, the topic of quarks and gluons will be as trivial as electricity is to us. We learn more every day, and examining its behavior helps us solve the riddle of the universe one measurement at a time.”

“We’re challenging and complementing humanity’s interest in knowledge and how matter behaves as you push it to its absolute limits. Confronting this challenging topic is the key to finally understanding all the unique ways matter manifests.”

- Jeannie Kever for College of Natural Sciences and Mathematics